(372b) Tof-SIMS: A Versatile Method for Zeolite Structure Detection

Microporous
crystalline aluminosilicate zeolites are widely studied for their applications in
catalysis, adsorption, purification and separation.  Throughout the
history of zeolite material development, its characterization mainly relies on
X-ray diffraction (XRD).  The XRD technique not only qualititavely identifies the
zeolite crystaline structure, but also quantitatively estimates a reliable  zeolite
phase purity. XRD can also be used to predict the chemical bonds and the
position of atoms inside the zeolite crystal. Despite its advantages, XRD is incapable
of verifying  zeolite crystalline structures with less than 4-5 unit cells in
size and less than 1 percent of zeolite content from the mixed phases. Other
characterizetion tools including
magic angle spinning
 NMR,
neutron diffraction, Raman specstroscopy and electron microscopy have
been developed to bridge the gap left by XRD.

This
work investigates the potential use of the Time-of-Flight Secondary Ion Mass Spectrum (ToF-SIMS), a surface-sensitive and
non-destructive method, to detect zeolite structures. Zeolites
secondary building units have been successfully detected by using the
technique. Here, Principle Component Analysis (PCA analysis), is employed to summarize
the main characteristics of zeolite in order to make predictive models. Utilizing
the data obtained from ToF-SIMS, PCA analysis can identify secondary building
units in zeolite samples. MFI type, ZSM-5 with exchangeable cations (H⁺, NH₄⁺,
Na⁺, K⁺), varied concentrations (from 0% to 100%), and Si/Al ratios (15 to ∞) has been
analyzed and the 5-1 ring structure of MFI has been consistently detected.